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Novolacs

Novolac (Novolak) Resins
The novolac are one of major classes of the phenolic resins (phenol formaldehyde resins), that are obtained by reaction of formaldehyde and phenol. The distinction of the classes are based on the reaction conditions that create two different polymers. One are resoles and other one are novolacs.

Chemistry

The novolacs resins are type on phenolic resins that are synthesised with presence of acidic catalyst and a molar excess of phenol to formaldehyde (1.4-1.9). There are variations of the synthesis using formaldehyde or formaldehyde derivatives. Because of formaldehyde exhibits high toxicity industry tend to avoid transporting it. The formaldehyde is used in the form of paraformaldehyde, solution in water, synthesized from methanol or used in form of methylene glycol.

Crosslinking

The novoloacs are thermoplastic polymer and for most applications need second component to be reacted for the improvement of the properties. Most of the the novolacs have to be crosslinked. The most common croslinkitng agent is Hexamethylenetetramine. Resole resins can be also used as crosslinker. Some other resins that are co-reacted are epoxy resins.

Application

Novolac resins find application in different industries where high temperature resistance is required. One of atypical applications, however with really high tonnage, is use as rubber tackifier. The tire industry is using enormous amounts of novolacs for this purpose. cit